1. Field of the Invention
This invention pertains generally to wireless communication data processing, and more particularly to proximity motion detection within wireless nodes, such as IEEE 802.11 wireless nodes.
2. Description of Related Art
The Open System Interconnection (OSI) standard provides a seven layered hierarchy between an end user and a physical device through which various network systems can communicate. Each layer is responsible for different tasks and the OSI specifies the interaction between layers while ensuring that the communication devices comply with the standard.
FIG. 1 shows the hierarchy 100 of the seven-layered OSI standard. As shown in the figure the OSI standard includes a physical layer 105, a data link layer 110, a network layer 115, a transport layer 120, a session layer 125, a presentation layer 130 and an application layer 135.
The physical layer 105 conveys the bit stream through the network at the electrical, mechanical, and functional level, therein providing a hardware means of sending and receiving data on a carrier. The data link layer 110 provides the representation of bits on the physical medium and the format of messages on the physical medium, sending blocks of data, such as frames, with proper synchronization. The networking layer 115 handles the routing and forwarding of the data to proper destinations, while maintaining and terminating connections. The transport layer 120 manages the end-to-end control and error checking to ensure complete data transfer. The session layer 125 sets up coordinates, and terminates communications between applications. The presentation layer 130 converts incoming and outgoing data from one presentation format to another. The applications layer 135 is where communications, quality of service, user authentication, and so forth are considered.
Similar to the OSI standard, the IEEE 802.11 committee has developed a three layer architecture for wireless networks that roughly corresponds to the physical layer, the data link layer of the OSI standard. FIG. 2 shows the IEEE 802 standard 160. As shown in the figure, the IEEE 802.11 standard includes a physical layer 165, a media access control (MAC) layer 170, and a logical link control layer 175. The physical layer 165 operates in a similar manner to the physical layer within the OSI standard. The MAC layer and the logical link control layers share the functions of the data link layer in the OSI standard 100. The logical link control layer 175 places data into frames that can communicate at the physical layer 165 and the MAC layer 170 manages communications over the data link, sending data frames and receiving acknowledgment (ACK) frames. Together the MAC layer 170 and the link control layer 175 are responsible for error checking as well as retransmission of frames that are not received and acknowledged.
The IEEE 802.11 MAC layer also defines the use of beacon frames being sent at regular intervals by an access point. The access point may act as a bridge between two networks with different protocols (e.g., Ethernet and 802.11 wireless networks).
Wireless technologies have been integrated into our daily lives and are being required to provide not only connectivity, but also high performance, reliability and stable communication. The most dominant of the 802 wireless communication standard is IEEE 802.11 and its variants, such as 802.11a, 802.11b, 802.11g which are being utilized in various wireless products. Communication between different nodes in an IEEE 802.11 based-network is performed by exchanging data frames between a sending node and a receiving node.
Each IEEE 802.11b frame transmitted from an IEEE 802.11 equipped device contains information including the signal strength of the frame and noise which may be measured to determine the source and destination of any particular frame. By measuring the signal strength information included in frames sent from a fixed node to a mobile node, it is possible to approximate the distance between fixed and mobile nodes.
However, wireless transmission under IEEE 802.11b are susceptible to the effects of multipath fading, wherein it can be very difficult to determine accurate location information for a node at any point in time. FIG. 3 illustrates a communication scenario 200 according to the IEEE 802.11 standards which are susceptible to the effects of multipath fading. As shown in the figure a transmission emitting from a base station 220 is transmitted by an antenna 210. The transmission may take a direct path to a receiving mobile node 230, or it may be reflected or diffused by one or more objects 240, 250, such as objects which are closer to antenna 210. The extent of multipath fading depends on the physical surroundings from which the multipath propagation of the signals directed towards receiving unit 230 arises.
In mobile wireless nodes the multipath propagation problem can be compounded by the motion of one of the nodes, providing a varying profile of multipath effects as at least one of the nodes moves in relation to the other. The occurrence of multipath propagation may cause the perceived signal strength information at a mobile node to fluctuate greatly as a result of the slightest movement of the mobile node or changes in the surroundings such as movement of obstacles in the line of sight. In 802.11b, beacon frames are periodically transmitted to synchronize multiple wireless devices. However, the use of periodical monitoring does not alleviate the inherent problem of IEEE 802.11 multipath fading.
Therefore, a need exists to monitor the signal strength in beacon frames in mobile devices to facilitate accurately determining their proximity relative to a stationary wireless target device. The present invention fulfills that need and others and overcomes numerous disadvantages with the prior art.